In the method known from EP 0 958 124 A each preform is rotated stepwise relative to the heat transfer element in order to produce the temperature profile. For instance, the preform is rotated by a rotational drive relative to stationary heaters or a cooling nozzle. The temperature profile is produced either by uniformly tempering the preform and overlaying it with the temperature profile, or the temperature profile is produced in the cold preform in a step-wise operation. The preform has a mechanically detectable circumferential marking, for instance, a groove in the support ring, so as to allow the adjustment of predetermined rotational positions of the preform or the blow-molded container. As the preform has to be rotated relatively fast and may already be plastically deformable the relative rotation may result in undesired deformations of the preform or in collisions with the heat transfer element, for instance, due to centrifugal forces.
In a method known from EP 1 279 477 A and an apparatus for the blow molding of bottles conceived to perform the method a non-contact sensor is used to detect grooves distributed on the preform in circumferential direction so as to precisely rotate each preform by rotation around the preform axis. In the blow mold the preform is engaged with protrusions provided in the mold by using the circumferential grooves.
In a method for blow molding oval bottles from basically circular cylindrical preforms according to U.S. Pat. No. 3,892,830 each preform is rotationally positioned by a rotatable holder relative to two diametrically opposite heat transfer elements, which are constructed as cooling jaws, before the cooling jaws are placed against portions of the circumferential surface of the preform in order to produce the temperature profile by heat abstraction. The temperature profile varying in the circumferential direction is produced to obtain a specific material distribution in the wall of the bottle during the blow molding of the non-circular contour shape of the circular cylindrical preform.